Photosensitized laminates find application in the printing and electronic circuit arts, and particularly for lithographic printing plates. Simply stated, the laminates (e.g. printing plates) comprise a substrate (usually metallic) and a photosensitive layer. Exemplary metallic substrates are aluminum, aluminum alloys, chromium and stainless steel. The composition of the photosensitive layer is such that when it is exposed to light, either (in a first type, e.g. bichromated colloid) the exposed parts become solvent (e.g. water) insoluble and remain when the unexposed parts are washed away by the solvent, or in the alternative, the unexposed parts are solvent insoluble and remain on the substrate, while the exposed parts have become solvent soluble and may be washed away. Depending on the nature of the composition and the image, i.e. whether the latter is positive or negative, either positive or negative images are formed on the substrate.
The images described above are generally receptive to inks, which are oil- or grease-based. Ink-receptivity may be improved, e.g., by application of lacquers. Moreover, in order to obtain clear prints from the images on the laminate surfaces, the non-image areas must be wettable by water, i.e. hydrophilic. Conventionally, a metal substrate is made wettable by anodic oxidation, see e.g. the anodization apparatus and process described in U.S. Pat. No. 5,314,607 (Kaneko et al.). The oxide layer thus formed on metal substrates giving rise to tenacious oxides (e.g. on aluminum or stainless steel) is intrinsically both stable and hydrophilic, whereas on zinc or iron, the oxide is not stable. It is well-known to stabilize zinc oxide surfaces by treatment with solutions of ammonium bichromate/sulfuric acid or ammonium alum/nitric acid. While an anodized (i.e. oxidized) surface of aluminum, if continuous and unbroken could be used without further treatment, once this develops faults it becomes unusable. In order to address this potential problem, anodized aluminum may be treated with e.g., a solution of ammonium bichromate/hydrofluoric acid. Alternatively, metal substrates may be made wettable by etching. It is known that aluminum, chromium and stainless steel may be etched satisfactorily with a solution of gum arabic/phosphoric acid, which is however too corrosive for zinc; in the latter case a solution of carboxymethyl cellulose sodium salt (CMC)/phosphoric acid/magnesium nitrate has been found to be suitable, but in this formulation a combination of tannic acid and potassium chrome alum (e.g.) may be used instead of magnesium nitrate.
The treatment described in the preceding paragraph results in the interposition of a hydrophilic layer between the metallic substrate and the photosensitive layer. The term “hydrophilic layer” in this context is intended to include both a single hydrophilic layer, and two or more adjacent hydrophilic sub-layers.
U.S. Pat. No. 6,207,349 (Lewis) discloses a procedure for easing interfacial transition between organic (polymeric) and inorganic layers in a lithographic plate by incorporating an inorganic component in a softened curable polymer deposited on a substrate, curing and depositing an inorganic layer thereover. The deposit of curable polymer may comprise a plurality pf sub-layers, each containing a different or graded proportion of the inorganic component. The inorganic layer may function as the hydrophilic layer in the lithographic plate.
In order to obtain relatively fine grained images and prints, it has become conventional to form a fine grain or crystal structure in the surface of the metallic substrate by abrasive, chemical and/or electrolytic treatment, referred to hereinafter as “graining”, while a surface not subjected to such treatment will be referred to herein as “ungrained”. Paradoxically, an alternative term for the same process is “roughening”. This procedure may be effected by wet or dry abrasion, using e.g., steel, alumina, sand, quartz or silicon carbide particles. U.S. Pat. No. 5,082,537 (Stroszynski et al) describes a combination of mechanical and electrochemical roughening, while e.g., U.S. Pat. No. 5,462,614 (Sawada et el.) and U.S. Pat. No. 4,585,529 (Kanda et al.), and U.S. patent application Ser. No. 10/655,369 published as 2004/0079252 A1 (Sawada et el.) mention mechanical, chemical and/or electrochemical surface graining.
U.S. Pat. No. 6,764,587 (Sawada, et al.) describes a process for producing an aluminum support for a planographic printing plate, by electrochemically surface-roughening the aluminum plate in an aqueous acidic solution; using an alternating current under prescribed conditions,
A variation of the above is the bimetal plate, usually copper electroplated on an aluminum or stainless steel substrate. The copper is ink-receptive and water-repellent, while the substrate is water-receptive and ink-repellent, i.e., hydrophilic. The copper surface is coated with a photosensitive layer and exposed to an object e.g. a negative. The unexposed parts of the photosensitive layer are removed, developing a coated image. Now the remaining copper (not part of the image composite) is removed by an etching liquid such as ferric chloride solution, which does not attack the underlying substrate. Any residue is cleaned with a mild abrasive which does not affect the developed image. Finally, the developed formerly photosensitive coating is removed leaving an ink-receptive copper image on the substrate. Similarly, U.S. Pat. No. 4,996,131 (Nouel) describes an offset printing plate comprising a hard, hydrophilic steel and deposited thereon a layer of dull, porous, ink-rejecting chromium (e.g. by contacting the steel base with a chromium-containing electrolytic solution and subsequently passing a current) having a thickness≦1 micron, of which a selected area may be removed subsequently, the chromium supporting a layer of photosensitive material.
U.S. Pat. No. 4,596,189 (Halpern et al.) describes a lithographic printing plate comprising a porous metal coating on a substrate and a light sensitive coating on the porous metal coating. The porous metal coating is produced by thermal spraying, and is typically 75 microns thick. After spraying, the coating is rolled to reduce the coating thickness to about half, while simultaneously closing the pores. The pores are reopened by removing part of the surface, e.g. by graining.
U.S. Pat. No. 3,839,037 (Fromson) describes a light-sensitive composite useful in the printing and electronic circuit arts, comprising a substrate and a light-sensitive coating thereon, and an ultra-thin light-transmitting and solvent-permeable protective coating over the light-sensitive coating, the protective coating being preferably a vapor-deposited metal coating.
U.S. Pat. No. 6,694,880 (Mori et al.) describes a printing plate provided with a material which is hydrophilic at a first temperature and hydrophobic at a relatively lower second temperature. The printing plate may include one or more of a defined group of simple or complex metal oxides.
U.S. patent application Ser. No. 10/653,928 published as 2004/0053167 A1 (Hotta) describes a method for the production of a support for a lithographic printing plate precursor that comprises providing on a grained aluminum support having an anodic oxide film formed thereon, a layer of inorganic compound particles having a major axis larger than a pore diameter of the anodic oxide film, and treating with a solution capable of dissolving the inorganic compound particles, which are thus fused together to form a layer of the inorganic compound. In a specified support, the ratio of pore diameter of the layer of inorganic compound to pore diameter of the anodic oxide film is not less than 1.5 and the ratio of F or Si of the layer of inorganic compound to the anodic oxide film is not less than 2.
U.S. patent application Ser. No. 10/743,412 published as 2004/0137365 A1 (Kawauchi, et al.) describes an infrared-sensitive lithographic printing plate capable of direct plate-making based on digital data from a computer or the like, comprising a support and a heat-sensitive layer, the latter comprising (A) a copolymer having a specific carboxylic monomer unit, (B) an alkali-soluble high MW compound having a sulfonamide group, and (C) a light-heat conversion material.
U.S. patent application Ser. No. 10/404,120 published as 2003/0194648 A1 (Murota et al.) describes lithographic printing plates comprising an aluminum substrate which has, on the surface, grained structures comprising medium waved structure whose average pore size ranges from 0.5. to 5 μm and small waved structure whose average pore size ranges from 0.01 to 0.2 μm (and optionally a large waved structure) which are superimposed.
The following patents and patent applications which have common ownership and/or common inventorship with the present invention, describe products and techniques which have relevance to the present invention.
U.S. Pat. No. 6,234,166 (Katsir et al.) describes a solar absorber-reflector, in which certain elements may be vacuum deposited aluminum or aluminum black.
U.S. Pat. No. 6,287,673 (Katsir et al.) describes and claims an anodized electrode, comprising an electrically conductive substrate. and a dielectric coating, on the surface of the substrate, having a bimodal morphology, in that the coating includes both a non-electrolytically formed valve metal oxide layer and an electrolytically formed layer, wherein the non-electrolytically formed layer is homogeneous and the electrolytically formed layer is increasingly porous towards its outer surface.
U.S. Pat. No. 6,764,712 (Katsir et al.) describes and claims a method for increasing the surface area of a substrate, comprising the steps of: (a) placing the substrate in an inert atmosphere, at 10−3 Torr to 10−2 Torr pressure, into which oxygen has been introduced at a pressure of from one to two orders of magnitude less than that just mentioned, and (b) evaporating at least one metal, selected from valve metals only, onto a heated substrate under said oxygen-containing inert atmosphere, whereby the product comprises a mixture of fractal surface structure including at least one valve metal and at least one valve metal oxide deposited on the substrate.
U.S. Pat. No. 6,933,041 (Katsir et al.) describes and claims an article of manufacture having a vacuum deposited fractal surficial structure, which includes both valve metal and an oxide thereof, the valve metal being selected from aluminum, titanium, tantalum, niobium, zirconium, silicon, thorium, cadmium and tungsten, as well as an electrode comprising:
(a) an electrically conductive substrate; and (b) a discontinuous vacuum deposited layer of an oxide of a first valve metal (selected from aluminum, titanium, tantalum, niobium, zirconium, thorium, cadmium and tungsten), on a surface of the substrate.
WO 0176768 (Acktar Ltd., Katsir et al.). describes a method and apparatus for temperature controlled vapor deposition on a substrate.
U.S. Pat. No. 6,865,071 (Katsir et al.) describes and claims integrated electrolytic capacitors and a method for making them.
In U.S. patent application Ser. No. 10/730,537 published as 2004-0168929 A1 (Katsir et al.), there is described and claimed an anodized electrode comprising: a substrate; a vacuum deposited porous coating thereon, comprising at least one substance selected from valve metals, valve metal oxides and their mixtures; and at least one electrolytically produced anodized layer selected from valve metal oxides and mixtures thereof; wherein in the porous coating, prior to electrolytic anodization, the effective surface area has been increased, e.g. by increasing the total pore volume of the porous coating, and/or by increasing the average pore width in the porous coating at its surface.
The entire contents of the above-mentioned patents and patent applications are incorporated by reference herein.